The present invention relates to a digital signal processing circuit for use, for example in a magnetic recording and reproducing apparatus for recording and reproducing a digital audio signal with the use of a rotary drum (hereinafter referred to as "digital audio tape recorder" or "DAT").
While such a digital audio tape recorder can record and reproduce an audio signal in high density with deterioration in the quality of sound effectively prevented from occurring, it is unavoidable that the overall structure becomes complex. Therefore it is the industry practice to arrange such circuit blocks as the digital signal processing circuit and the servo circuit in integrated circuits to thereby simplify the overall structure.
Generally, in digital audio tape recorders, the magnetic heads are disposed on a rotary drum, having a diameter of 30 mm, at an angular distance of 180.degree. and a magnetic tape is wound around the rotary drum at a wrap angle of 90.degree..
However, it is possible to miniaturize the DAT if an arrangement made up of a rotary drum being 15 mm in diameter with magnetic heads disposed thereon at an angular distance of 180.degree. and a magnetic tape wound around the same at a wrap angle of 180.degree. is used. With this arrangement, it is possible to obtain similar record tracks to those obtained with the use of the rotary drum being 30 mm in diameter.
However, when a rotary drum of 15 mm in diameter is used, the record signal must be supplied to the magnetic heads disposed on the rotary drum at a different timing from that when a rotary drum of 30 mm in diameter is used.
That is, there arises a problem that such a digital signal processing circuit becomes necessary which will output the record signal at a different timing depending on whether the rotary drum of 30 mm in diameter is used or the rotary drum of 15 mm in diameter is used.
As a measure to solve such a problem, it is considered to add a specific converter circuit to the digital signal processing circuit for changing the timing of the output so that only one type of digital signal processing circuit need be used for the cases where the rotary drum is 30 mm in diameter or 15 mm in diameter. In such a case, however, the overall structure becomes accordingly complex. Further, duplicated circuit portions are required in the converter circuit and the digital signal processing circuit and therefore, this arrangement is still insufficient for practical use.